The present invention relates to slurry distribution grooves in a polishing pad employed in chemical mechanical polishing (CMP). More particularly, the present invention relates to cross-sectional groove shapes which increase the slurry carrying capacity of a polishing pad and improve the pad's surface hardness characteristics.
Chemical mechanical polishing (sometimes referred to as "CMP") typically involves mounting a semiconductor wafer faced down on a holder and rotating the wafer face against a polishing pad mounted on a platen, which in turn is rotating or moving linearly or orbitally. A slurry containing a chemical that chemically interacts with the facing wafer layer and an abrasive that physically removes that layer is flowed between the wafer and the polishing pad or on the pad near the wafer. In semiconductor wafer fabrication, this technique is commonly applied to planarize various wafer layers such as dielectric layers, metallization layers, etc.
FIG. 1 shows some major components of a chemical mechanical polishing (CMP) apparatus such as an AvantGaard 676, commercially available from Integrated Processing Equipment Corporation (IPEC) of Phoenix, Ariz. CMP apparatus 100 includes a wafer carrier 128 that is fitted with an air chamber 126 (shown in phantom lines), which is designed to secure a wafer 124 by vacuum to wafer carrier 128 during wafer loading typically before CMP is to commence. During CMP, however, wafer 124 is bound by "wear rings" (not shown to simplify illustration) within wafer carrier 128 such that a wafer surface that is to be polished contacts a polishing pad 102.
A conventional polishing pad 102 includes a plurality of slurry injection holes 120, and adheres to a flexible pad backing 104 which includes a plurality of pad backing holes 118 aligned with the slurry injection holes 120. A slurry mesh 106, typically in the form of a screen-like structure, is positioned below the pad backing 104. An air bladder 108 capable of inflating or deflating is disposed between a plumbing reservoir 110 and the slurry mesh 106. A co-axial shaft 112, through which a slurry inlet 114 (shown by phantom lines) is provided to deliver slurry through the plumbing reservoir 110 and the air bladder 108 to the slurry mesh 106, is attached to the bottom of plumbing reservoir 110. In this configuration, a slurry flow path is defined by the slurry entering through slurry inlet 114, spreading out through the slurry mesh 106 below the pad backing 104, entering pad backing holes 118 and exiting through slurry injection holes 120 on the surface of polishing pad 102.
A CMP pad is typically provided with grooves in its polishing surface for slurry distribution and improved pad-wafer contact. These grooves are of two types, either or both of which may be present on a conventional pad's polishing surface. The smaller of the two groove types, sometimes referred to as "microgrooves," are typically about 10 mils wide and 10 mils deep. Microgrooves increase the pad roughness and thereby facilitate the polishing process by creating point contacts and providing space for a small amount of slurry at the wafer-pad surface interface during CMP. Larger or "macrogrooves" (also referred to as slurry distribution grooves) increase the amount of slurry that may be applied to the polishing pad surface per unit area, and thereby increase CMP efficiency. Conventional macrogrooves are typically about 50 mils deep by 50 mils wide.
FIG. 2 shows a top view of a conventional polishing pad 102, such as used with the CMP apparatus shown in FIG. 1. An example of such a pad is the IC 1000, commercially available from Rodel Inc., Newark, Del. Polishing pads may be made of materials including, for example, urethane, polyurethane, felt, polymer and a filler material. Polishing pad 102 includes macrogrooves (slurry distribution grooves) 130, which are shown in an X-Y configuration, and microgrooves 132 which oriented diagonally relative to macrogrooves 130. At various intersections of grooves 130 in the X direction and grooves 130 in the Y direction, slurry injection holes 120 are provided.
In conventional chemical mechanical polishing pads, slurry distribution grooves in the polishing pad surface have substantially parallel side walls. Cross-sectional views of such conventional groove shapes are shown in FIGS. 3A-3C. In FIG. 3A, groove 300 has substantially parallel side walls 302, 304 extending down from the polishing pad surface 306 to the pointed base of the groove 308. The span 310 of the surface opening 312 of the groove 300 is substantially the same as the maximum sub-surface span 314 of the groove 300.
FIGS. 3B and 3C show alternative conventional groove cross-sections 320 and 330, respectively, having flat and rounded bases 322 and 332, respectively. As with groove 300, grooves 320 and 330 have surface opening spans 310 substantially the same as their maximum sub-surface spans 314.
Conventional chemical mechanical polishing pad slurry distribution grooves such as those illustrated in FIGS. 3A-3C are typically formed by incising cuts in the polishing surface of a chemical mechanical planarization polishing pad. Common apparatuses for making these cuts include saws, mills, and lathes. The substantially parallel side walls 302 and 304 of these conventionally shaped grooves are generally a function of the profile of the cutting blade which forms them.
A CMP pad will have a surface hardness largely determined by the material from which it is formed and any structural alterations made to the pad surface. While conventional groove patterns may provide some regional flexibility beyond that normally characteristic of a particular pad material, conventional pads have substantially uniform hardness across their surfaces. This uniformity may result in the formation of pits in the surface of a polished wafer, adjacent to bumps removed during CMP, due to the inability of the pad to conform somewhat to the wafer topography. Such pit formation detracts from the quality of the planarization of the wafer surface that may be achieved by CMP.
Thus, while conventional slurry distribution grooves increase the slurry carrying capacity of CMP pads, a CMP pad with a groove design that improved slurry carrying capacity over conventional designs and thus improved CMP efficiency, would be desirable. Additionally, a pad having a hardness optimized to reduce bumps in a wafer surface while minimizing the development of pits during polishing is needed.